4. WR Kyle Williams

Kyle Williams experienced the dread all athletes wish to avoid when he tore his anterior cruciate ligament against the Saints in Week 12. He had amassed 212 yards receiving and one touchdown up to that point.

While those may seem like pedestrian numbers, Williams was a consistent deep threat for San Francisco. Two prime examples were his 43-yard touchdown against the Bills and a 57-yard tone-setter in the 49ers’ 32-7 win over Chicago.

Both receptions were highly impactful in the early goings of each game. His speed, reliable hands and short-area quickness out of the slot were valuable assets to the passing game overall.

Williams started Week 1 against Green Bay and logged 16 offensive snaps. He showcased his versatility with a carry out of the backfield and solid blocking in the run game.

Despite not registering a catch, his presence created opportunities for other offensive weapons on San Francisco. Randy Moss and Mario Manningham piggybacked off Williams’ start and logged eight receptions and a touchdown.

Without him, the 49ers must now turn to Ted Ginn and rookie A.J. Jenkins against the Packers in a prime-time playoff matchup.

Ginn is normally a return man and is completely ineffective as a receiver (two catches for one yard). Worse yet, Jenkins dropped the only pass thrown his way and wasn’t supposed to see meaningful action until 2013.

And lest we forget, Williams led San Francisco with a 27.2-yard average on kickoff returns, not to mention a 94-yarder against the Vikings.

Williams, the 49ers wide receiver that once held the No. 4 slot on the depth chart, would suddenly find himself in loftier echelons were he to be available on Saturday.

3. WR Mario Manningham

The first-year 49er one-upped his wide receiver counterpart by tearing both his ACL and PCL after a gruesome gang-tackle by the Seahawks defense two days before Christmas.

Outside of Michael Crabtree, Mario Manningham was the most consistent receiver for San Francisco. He averaged roughly four receptions and 40 yards per game as the No. 2 wideout. His totals came out to 42 catches for 449 yards and one touchdown in 12 starts.

Again, those aren’t numbers that resonate with any surface value. But Manningham was a versatile, sure-handed target who could play every down.

He dropped only one pass (via Pro Football Focus) all season long and showed big-play abilities as a ball-carrier in the 49ers’ diverse run formations (two end-arounds that gained 28-plus yards).

Manningham could do it all as a secondary receiver in a run-first offense.

With he and Williams gone, Moss’s role increases beyond all expectations that the 49ers had for the veteran wideout. Starting every game means diminishing his effectiveness as a downfield target used on selective downs (see: TD catch against Packers).

That in turn places more pressure on Crabtree while forcing tight end Delanie Walker to serve as the No. 3 WR in the playoffs—possibly against Green Bay’s shutdown slot corner Casey Hayward.

Walker is an essential blocker, and at times, a dynamic playmaker, but his penchant for dropped passes is far too disconcerting.

He allowed a game-clinching touchdown pass to sail through his hands against St. Louis and ranks third among NFL tight ends with nine drops (via Pro Football Focus).

See how quickly a once deep offensive team transforms into one that’s wholly depleted?

2. RB Kendall Hunter

Jeff Hanisch-USA TODAY SportsKendall Hunter rushed for 40-plus yards for San Francisco the first time around.

Shall we continue with the theme of systematic human destruction on the football field?

Kendall Hunter injured his Achilles on the very same play that produced a tear of Williams’ ACL during the Saints game.

At first glance, the severity of the injury wasn’t readily apparent. Yet, shortly after the inevitable news of Williams’ status became public knowledge, San Francisco trainers deemed Hunter lost for the season.

And just like that, the perils of the NFL gridiron claimed the most underrated piece to the 49ers puzzle.

Hunter is a 5’7’’, 199-pound running back whose role in this offense gets repeatedly overlooked. Too often people view him as an ordinary second-stringer and basic change-of-pace back.

Fortunately for him, we’re in the business of giving credit where credit is due.

Hunter is a multi-dimensional talent who performs a wide array of functions from the running back position. He can stretch defenses to the outside with his speed, while using his short-area burst and small stature to carve rushing lanes between the tackles.

He’s also a viable, if not, dangerous threat catching balls out of the backfield when called upon.

Most of all, though, Hunter was the perfect complement to Frank Gore. He kept the veteran fresh by providing six to seven carries per game. He did so without the 49ers missing a beat offensively, evidenced by his average of 5.2-yards per carry, 431 total yards and two touchdowns.

(Not to mention just one lost fumble.)

Appropriately enough, Hunter played some of his best football against Green Bay in Week 1. He helped establish a dominant running game for the 49ers and nearly out-rushed the entire Packers team by himself.

His nine carries also helped Gore rush for 112 yards on an economical 16 attempts. That tandem was a huge reason why San Francisco won that game.

Hunter’s absence places considerably more strain on Gore—the vital conduit to the 49ers’ success on offense. It also thrusts rookie LaMichael James into the spotlight.

Don’t get us wrong—James has been incredible with a 30-yard average on kickoffs, especially with his 62-yarder that set up the game-winning drive at New England. His 4.6 yards per carry is solid as well.

But, the certainty Hunter brought with him on the playoff stage does not yet exist with James. We cannot know for sure how he’ll fair when spelling Gore against the Packers.

At the end of the day, the age-old principle of next man up can only take so much sting out of yet another devastating injury.

1. QB Alex Smith

Ezra Shaw/Getty ImagesColin Kaepernick will lead the charge for San Francisco on Saturday. Can he do it?

Note: Please temper any and all outrage for just a second.

This is not the uplifting of one quarterback at the expense of another. We aren’t declaring that either 49ers QB is better than the other or why one is playing and why one is not.

We’re merely pointing out a personnel change at the most important position on the field and evaluating the one calling plays in the huddle.

On opening week, Alex Smith put forth arguably his greatest quarterbacking of the season against the Packers.

Smith’s 83.5 QBR and 8.12-yards per completion both ranked as third highest for him in 2012. He surpassed his 76.9 completion percentage just once.

What made the performance so special, however, were his two touchdowns and zero interceptions (and 221 yards) in a battle for NFC supremacy in enemy territory. Smith executed a balanced game plan to perfection, outplaying Aaron Rodgers at Lambeau Field in the process.

Starting Saturday, January 12, at 5 p.m. ET, Colin Kaepernick, and not Alex Smith, will take the field under center.

And the only real question that needs answering, then, is whether Kaepernick can lead a similar winning performance against the Packers, albeit in the playoffs.

Since we don’t fancy ourselves masters of the human psyche, we’ll keep it simple. Let’s break it down using empirical data from Kaepernick’s greatest outings of the season.

Kaepernick made his first career NFL start against the 7-2 Bears at Candlestick Park. He completed 69.6 percent of his passes for 243 yards, two touchdowns and zero interceptions. He produced a QBR of 97.5 and averaged 10.57-yards per pass.

The Bears featured one of the most formidable pass defenses in the league at that point.

Against the 10-3 Patriots on their home turf, Kaepernick completed just 56 percent of his passes and threw an interception. He did, however, throw four touchdowns and put up an 87.7 QBR and average of 8.84-yards per pass.